30 Wall-Rue 



the formation of another rachis, the base of this leaflet, contain- 

 ing the part of the vein that enters the leaflet below the first fork- 

 ing of that vein, becomes elongate and forms the part of the new 

 rachis between its first leaflet and the old rachis. 



The part in general taken by the venation in the leaf -develop- 

 ment wUl be more readUy understood by studying PI. I, Fig. 2. 



Many of the leaflets of the leaves of the older plants are more 

 or less incised between the marginal veinlets. This incision, to 

 which is due the peculiar toothed appearance seen so often in 

 this fern's leaves, is not to be confused with the incision described 

 above, employed in the leaf-development. 



The plants bear sporangia when very young. The bifoliate 

 leaf is sometimes fertile. 



A. ruta-muraria has been included in the genus Asplenium 

 by nearly all pteridologists. Newman, however, in 1844, sepa- 

 rated it from Asplenium, to form, together with A. septentrionale 

 and A. germankum, a genus which he named Amesium. But 

 A. septentrionale had aheady stood as the type of a genus of 

 Mirbel's. * The afi&nity of A . ruta-muraria with A . septentrionale 

 appears very marked, especially on comparing the leaf-devel- 

 opment of the two species, and, taking into consideration the 

 flabellate venation and other peculiarities which characterize 

 these two species, they appear sufficiently distinct to warrant 

 restoring Mirbel's genus Belvisia and including A. ruta-muraria 

 in it. 



* Belvisia Mirb. in Lam. & Mirb. Hist. Nat. Veg. 3: 405. 1802. 



